If you want to apply it to specific pages, then the simplest method is to:
1. Install the Simple CSS plugin:
https://en-gb.wordpress.org/plugins/simple-css/
2. Edit the Pages you want to change the nav colors and add this CSS in the Simple CSS meta box:
.main-navigation, .main-navigation ul ul {
background-color: #000;
}
.main-navigation .main-nav ul li a, .menu-toggle, .main-navigation .menu-bar-items {
color: #fff;
}
/* Set Hover colors */
.main-navigation .main-nav ul li:hover a,
.menu-toggle, .main-navigation .menu-bar-items:hover a {
color: #f00;
background-color: #222;
}